The Lord said unto Moses This seems to have been a second vision, whereby God calls him to the present execution of the command given before. The rod of God His shepherd's crook, so called, as it was God's instrument in so many glorious works.
Related Commentaries of Exodus 4:19
Exodus 4:19-20
19 And the LORD said unto Moses in Midian, Go, return into Egypt: for all the men are dead which sought thy life.
20 And Moses took his wife and his sons, and set them upon an ass, and he returned to the land of Egypt: and Moses took the rod of God in his hand.